Masking effects on Iso-valeric Acid Recognition by Sub-threshold Odor Mixture

Masking unpleasant odors with high levels of pleasant-smelling odorants is an ancient practice that has evolved into many enterprises, from perfumery to consumer products. However, effective odor masking turns out to be idiosyncratic and impermanent. Here, we used Sniff Olfactometry (SO)(Rochelle et al., 2017; Wyckoff & Acree, 2017) to investigate the psychophysics of masking during 70ms-stimulations with mixtures of the mal-odorant iso-valeric Acid (IVA) and different masking agents. IVA is a component of human sweat that can dominate its smell, and is often described in unpleasant terms, e.g., "gym locker", "smelly feet", "dirty clothes", etc. Conventionally, high concentrations of positive smelling odorants are used to reduce the unpleasantness of IVA in clothing or environments contaminated with IVA. To investigate the masking effects of sub-threshold levels of masking agents (neohivernal, geraniol, florhydral, decanal, iso-longifolanone, methyl iso-eugenol, and s-limonene) on IVA, we used SO to measure the probability of recognizing IVA after 70ms stimulations with headspaces containing mixtures of super-threshold concentrations of IVA and sub-threshold concentrations of IVA-suppressors for 9 subjects. On average, the single masking agent could decrease IVA-recognition probability by 14% to 72%, and a subthreshold odor mixture consisting of 6 masking agents decreased IVA recognition by 96%.